1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive employing different zone boundaries across disk surfaces.
2. Description of the Prior Art
Prior art disk drives employ one or more disks with heads actuated over the respective disk surfaces (e.g., top and bottom surfaces). Each disk surface comprises a plurality of radially spaced, concentric data tracks, wherein each data track comprises a number of data sectors for storing user data. During write operations, the disk drive receives user data and a logical block address (LBA) which is mapped to an absolute block address (ABA) identifying one of the data sectors for storing the user data. The LBA to ABA mapping enables defective data sectors to be mapped to spare data sectors.
Because the disk is rotated at a constant velocity, the data rate is typically increased toward the outer diameter tracks (where the surface of the disk is spinning faster) in order to achieve a more constant linear bit density across the radius of the disk. To simplify design considerations, the data tracks are typically banded together into a number of physical zones, wherein the data rate is constant across a zone, and increased from the inner diameter zones to the outer diameter zones. This is illustrated in FIG. 1, which shows a prior art disk format 2 comprising a number of data tracks 4, wherein the data tracks are banded together in this example to form three physical zones from the inner diameter of the disk (ZONE 1) to the outer diameter of the disk (ZONE 3). The prior art disk format of FIG. 1 also comprises a number of embedded servo sectors 60-6N recorded around the circumference of each data track. Each servo sector 6i comprises a preamble 8 for storing a periodic pattern, which allows proper gain adjustment and timing synchronization of the read signal, and a sync mark 10 for storing a special pattern used to symbol synchronize to a servo data field 12. The servo data field 12 stores coarse head positioning information, such as a track address, used to position the head over a target data track during a seek operation. Each servo sector 6; further comprises groups of servo bursts 14 (e.g., A, B, C and D bursts), which comprise a number of consecutive transitions recorded at precise intervals and offsets with respect to a data track centerline. The groups of servo bursts 14 provide fine head position information used for centerline tracking while accessing a data track during write/read operations.
Prior art disk drives typically configure the physical zones so that the zone boundaries occur at the same radial locations across all disk surfaces. However, a recent development is to optimize the size of each physical zone relative to the characteristics of each head/disk interface. In addition, the linear bit density as well as the tracks-per-inch (TPI) may be optimized for each disk surface, which can also cause the size of the physical zones (and corresponding physical zone boundaries) to differ across the disk surfaces. When the physical zone boundaries are different across the disk surfaces, a problem arises in locating the appropriate data sector corresponding to a given ABA. In other words, allowing the physical zone boundaries to vary across disk surfaces complicates the process of mapping an ABA to the corresponding physical zone, head, and data track.
There is, therefore, a need to simplify the ABA to zone/head/track mapping in a disk drive wherein the zone boundaries vary across the disk surfaces.